Heretofore, known instruments for aiding in the use of maps, such as exemplified in Hotchkiss U.S. Pat. No. 4,337,577 dated Jul. 6, 1982 and Lambert, U.S. Pat. No. 4,359,628 dated Nov. 16, 1982, are very limited in their usefulness, particularly for military purposes. One such limitation is that they are applicable to a single scale map because each instrument is calibrated for use with one of several military scaled maps, as for example 1:25,000, 1:50,000 or 1:125,000. Another limitation of known instruments, particularly for military uses, is that the user has a need in the effective use of a map to make arithmetical computations and, therefore, military recruits must undergo extensive training in map reading. Some of the arithmetical computations involve converting magnetic azimuths to grid azimuths and conversion to back azimuths when it is desired to locate on the map an unknown point from two known points, which functions are referred to as "resection" and "intersection". Also, in determining the total distance along a sinuous path, e.g. a road or railroad track, the user must add the straight portions of the path between the curved portions. A further limitation of known map reading devices is that the artillery uses instruments in which angular directions are measured in mils rather than degrees for more accurate aiming of the weapons. Thus, artillery personnel and those spotting for artillery units must have special map reading and plotting instruments. Obviously, where in the use of heretofore known map reading instruments computations are required, the need for paper and/or a writing implement poses a problem, particularly under actual field conditions where paper and a writing tool is not always available to the map user. Also, map reading and plotting instruments of heretofore known types require the user to draw lines on a map and, in absence of available paper, the user may use the map for making computations. These writings on a map lead to short map life and leaves marks which even if erased, are visible or can be made visible and may give aid to an enemy if the map is captured.